Our proposed research focuses on defining how Helicobacter pylori locates and uses a particular nutrient in the mammalian stomach. There is a gap in our understanding of the metabolism used by H. pylori to thrive in the gastric environment. Millions of people worldwide and in the U.S. are infected by H. pylori and suffer from its associated diseases?ulcers and gastric cancer. Gastric cancer is the second cause of cancer deaths worldwide. H. pylori will be an on-going problem, as the incidence has stabilized in the developed world. Fur- thermore, current therapies to cure H. pylori infection fail with unacceptable frequency, e.g., recent estimates in the United States have found that 20-25% of infected individuals are not cured by the current therapeutic re- gime. To thrive in the stomach, H. pylori must obtain nutrients. Published and preliminary data show that H. pylori chases down one interesting nutrient, lactate using chemotaxis. The bacterium furthermore uses it as a top choice for promoting growth. The overall objective of this application is to understand when and where H. pylori locates and uses lactate during infection. Our overall hypothesis is that H. pylori locates lactate-enriched regions with a specific chemotaxis sensing protein called TlpC, which has been shown to bind lactate. The bacteria then uses specific proteins of the lactate uptake pathway to utilize lactate for growth. In Aim 1, we will create and analyze H. pylori strains with non-lactate-sensing TlpC variants to see how these alter colonization in stomachs. In Aim 2, we will determine the cellular source of lactate during H. pylori infection. In Aim 3, we will analyze the roles of lactate metabolic proteins in host colonization. The proposed research is innovative in its hypothesis that H. pylori seeks lactate using chemotaxis and that gastric pathogens push the host toward producing lactate. The proposed research is significant because it will provide new insights into colonization mechanisms of an important bacterium, H. pylori, that causes significant and on-going health problems, but for which we lack sufficient antibiotic efficacy. The work will furthermore provide an understanding of new strate- gies used by bacteria to establish nutritional niches within mammalian hosts. The long-term outcomes gener- ated by this research will provide insights that may enable creation of new drugs against H. pylori-related dis- ease.